The present invention is directed to an improvement in an indexing vacuum-packaging machine. Examples of such conventional vacuum packaging machines are disclosed in applicant's U.S. Pat. Nos. 5,271,207 and 5,517,805, for example, which references are incorporated by reference herein.
In a conventional, indexing vacuum-packaging machine, a lower film-web is indexed using an indexing advancing mechanism for situating the transverse, multiple package-receptacles formed in the lower film-web at a forming station and then to a sealing or sealing/vacuum station, where the upper film for completing the packages is applied, and vacuum-sealed. At each station, a lower tool is raised toward an upper, stationary tool for performing the requisite tasks at the respective station. However, in all indexing vacuum-packaging machines, misalignment between the upper and lower films is inevitable, owing to the fact that the longitudinal length of the lower film, taken in the direction of the indexing, constituting the length of each finished vacuum-package, after the cutting at the final cutting station, is greater than the length of the upper-film portion constituted by the printed matter, which printed matter typically consists of a repeating pattern of the name of the product contained in the package, the weight and/or quantity thereof, bar code, unique designs, and the like. This length of the printed matter on the upper film is intentionally made shorter than the length of the lower-film package-length, in order that the upper film may be slightly stretched at the vacuum-sealing station, in order to form a tight vacuum seal.
The material from which the upper is made is flexible and stretchable, which allows of the stretching thereof. In a conventional vacuum-packaging machine, the upper film is stretched every indexing cycle by means of brakes applied to the upper film at the sealing station. However, it is not possible to stretch the upper film in such a precise manner as to ensure continuous and proper registration and alignment of the upper film with the lower film in both the longitudinal and transverse direction relative to the lower film. Thus, longitudinal mis-registration, as well as transverse misalignment, is inevitable. The amount of stretching of the upper film is controlled and determined by the use of a dedicated photocell mounted above the indexed upper film at the sealing station. This photocell typically detects one black target-box per indexing cycle imprinted on the upper film, as mentioned above. This one, black target-box is located longitudinally centrally of the printed matter, at the end of the portion of the repeating pattern constituting the upper film of the central or middle package of the multiple packages being formed simultaneously at the sealing station. This black box of the printed matter of the upper film is used to indicate the end of the printed matter for each indexing cycle, and, therefore, the end of the length of the upper film to be sealed to the lower film at the sealing station. The photocell uses this black target-box to ensure that longitudinal registration is maintained between the upper and lower films for each indexing cycle. Thus, when the photocell detects that black target-box during each indexing cycle, it outputs a signal to cause the braking mechanism at the sealing station to brake the upper film for a predetermined time period in order to stretch the upper film the requisite amount in order to increase the length of the portion of the upper film between the upper-film supply and the portion of the upper film sealingly connected to the lower film at the sealing station during the previous indexing cycle. Ideally, this braking will stretch the upper film the exact amount equivalent to the difference between the length of the lower film at the sealing station containing the multiple, transverse receptacles formed simultaneously by the indexing machine during each indexing cycle and the length of the printed matter on the upper film. However, in reality, this is not case. This is so, because the photocell used for detecting the black target-box does not typically have a high resolution, and will often detect other printed matter on the upper film and assume that it is the target box. Moreover, since application by the brakes every indexing cycle creates formidable and considerable forces and jerking of the entire machine, transverse, or lateral, shifting, or creeping, of the upper film occurs, thus causing lateral or transverse misalignment between the edges of the upper and lower films. Since there is only black target-box imprinted on the upper film for each indexing cycle, at the center position of the upper film constituting the center, or middle, package being formed during the indexing cycle, it often occurs that the photocell will not detect any printed matter at all during any indexing cycle, or will interpret other printed matter as being the target. Thus, that indexing cycle will produce ill-formed packages, necessitating the operator of the machine to stop the machine, to remove the contents of the packages formed during that indexing cycle, and to reset or re-align the upper film so that the photocell will again be able to detect a black target-box the next indexing cycle. This problem has led to considerable downtime of the packaging machine, and the concomitant loss of productivity.
FIGS. 1 and 2 show the sealing station of a conventional vacuum-packaging machine, where the upper film layer and the lower film layers, forming the horizontal row or rows of filled vacuum-packages, are heat-sealed together via an upper heating tool after the rectangular-shaped lower and upper tools of the sealing station have been brought against each other, and after a vacuum has been formed in the each package of the row of packages. A sealing station 20 consists of a supply 36 of upper plastic film 22 constituting the upper layer of the finished vacuum packages and is unrolled to a location juxtapositioned above the product-filled pocket-receptacles of the lower film. The upper film 22 is delivered to the sealing station proper via guide rollers 40, 42, 44, and 46, it being understood that a conventional tensioning arm or arms are provided in the usual manner for controlling tension of the transported film. At the sealing station 20, the upper film is heat-sealed to the lower film, during which sealing a vacuum is formed in the packages via a nozzle-head 28. The sealing station has an upper chamber 24 in which is mounted for relative movement a heating tool 25, which heating tool has a lower projecting perimetric, or peripheral, heating element 25′. The upper tool abuts against a lower tool 26 when the upper and lower tools are brought into abutting contact against each other during the sealing process during each indexing cycle, with upper and lower tools holding the upper film and lower films, respectively, by suction. Either the upper tool 24 or lower tool 26 may be movable toward the other, with the other usually being stationary. The number and rows of vacuum packages being sealed at the sealing station will vary depending upon the product. For example, there may be two rows of four vacuum packages for each row being heat sealed at the sealing station. The lower tool will have the appropriate mold configuration depending upon the number of rows and number of packages per row. During each indexing cycle, the supply film 22 is stretched by a braking mechanism (not shown) in order to stretch the length thereof, in the manner described hereinabove.
Referring to FIG. 4, there is shown a longitudinal and transverse section or portion of conventional upper film 22 used in a conventional vacuum-packaging machine in which has been imprinted a transverse, or lateral, repeating pattern 52 of printed matter 50, with each repeating pattern 52 constituting the printed matter on the upper film-layer of a finished vacuum-package with contents. The number of repeating patterns 52 is equal to the number of lateral packages formed in the lower film at the forming station. Each repeating pattern 52 of the printed matter 50 may typically consist of the following: contents of the package, weight and/or quantity of the contents, bar code, name of manufacturer, logo or trademark, and the like. In addition, the printed matter 50 also consists of one, longitudinally and centrally located black target-box 54 used for detection by a photocell, as described above.